Low-temperature physical properties of Ba ₈Ni _x Ge _46-x (x = 3, 4, 6)

Polycrystalline samples of type I clathrate Ba ₈Ni _x Ge _46-x (x = 3, 4, 6) have been synthesized using a radio-frequency (RF) induction furnace. Ba ₈Ni _x Ge _46-x samples show metallic-like behavior (dρ/dT > 0) with high resistivity at room temperature, and diamagnetic susceptibility at 2 K and 300 K. The charge carriers vary from n type to p type depending on the Ni stoichiometry. The carrier concentrations at 300 K are calculated to be 5.84(3) e ^-/cell for x = 3, 2.29(1) e ^-/cell for x = 4, and 3.29(1) h ⁺/cell for x = 6. The deviation of the carrier concentrations from the values expected based on 4-bonded Ni suggests that vacancies may play a very important role in the electronic states. The effective carrier masses are estimated from the low-temperature heat capacity data.